Phenotypic variability associated with another variant in cis is exemplified by the presence of XAF1 p.E134∗ in a subset of TP53 p.R337H carriers (Hap1) that are at higher risk of cancer in general, sarcomas, and multiple tumors compared with those with TP53 p.R337H alone (Hap2).8 The gene discussed is TP53; the disease is cancer.